1. Field of the Invention
This invention relates to a core of a solenoid actuator for electromagnetically driving a driven member, and more particularly to a multilayer core formed by a laminated stack of a plurality of magnetic plates.
2. Description of the Prior Art
Conventionally, a solenoid actuator of this kind has been proposed e.g. by Japanese Laid-Open Patent Publication (Kokai) No. 11-273945, which is applied to a valve-actuating mechanism for opening/closing a valve (gas exchange valve) of an internal combustion engine, and includes an armature and upper and lower electromagnets for vertically attracting the armature.
Each of the electromagnets includes a core having an E shape in cross section. The recessed portions of the E-shaped core serve as a coil groove opposed to the armature and accommodating a coil. The core is a unitary assembly formed of a center core member and a multiplicity of laminates stacked on opposite sides of the center core member. The center core member is formed of silicon steel which is larger in thickness than each laminate and has an E shape in side view. The laminates are each formed of a composite magnetically soft material having the same shape and size as those of the side face of the center core member and are stacked on the opposite sides of the center core member as described above. The center core member and the multiplicity of laminates are welded together to form the unitary component, and the end faces of the center core member and the laminates opposed to the armature form a flat attracting surface for receiving the magnetically attracted armature thereat. The reason why the core (laminated core) having the multilayer construction described above is employed is that it is possible to reduce core loss during energization of the electromagnet compared with the case of a solid core is used, thereby ensuring high energy efficiency.
The armature is connected to the valve via a shaft, and a during operation of the solenoid actuator, the armature is attracted alternately by the upper and lower electromagnets to reciprocate vertically to open and close the valve. The armature attracted by the upper and lower electromagnets during the operation of the solenoid actuator is brought into abutment with the attracting surfaces of the cores of the electromagnets.
Therefore, the above conventional cores of the solenoid actuator suffer from the problem that impact of the abutment of the armature on each core during operation of the solenoid actuator can cause weld crack, thereby causing deformation and breakage of the laminates, which results in malfunction of the solenoid actuator. Further, laminates at opposite ends of the core, which are formed of the magnetically soft material, generate magnetic fields between magnetically soft components around the core and themselves during energization of the electromagnet, whereby part of energy of the electromagnet is lost.
It is an object of the invention to provide a core of a solenoid actuator, which is improved in durability, and at the same time ensures high energy efficiency of the solenoid actuator.
To attain the above object, the present invention provides a core of a solenoid actuator, for attracting an armature during operation of the solenoid actuator, comprising:
a plurality of core plates made of a magnetically soft material and stacked in a predetermined direction orthogonal to a direction of attracting the armature to form a laminated stack, for forming magnetic circuits between the armature and the core plates themselves during the operation of the solenoid actuator;
two core holders formed of a non-magnetic material and sandwiching the laminated stack of the plurality of core plates from opposite sides along the predetermined direction;
an insulator interposed between each adjacent two of the plurality of core plates, for insulating the each adjacent two core plates from each other; and
fixing means rigidly securing the plurality of core plates and the two core holders to each other to form a unitary assembly.
According to this core (including a yoke forming a magnetic circuit between the armature and the yoke itself) of a solenoid actuator, a stack of the plurality of core plates sandwiched between the two core holders is fixed by the fixing means to form a laminated stack. The plurality of core plates are stacked in the predetermined direction orthogonal to the direction of attracting the armature, in a state insulated from each other by the insulators, a magnetic circuit is formed between each core plate and the armature during the operation of the solenoid actuator, and at this time, an eddy current is generated in each core plate. However, since the core of the invention is formed by the plurality of core plates each of which is thinner than an ordinary solid core, the eddy current generated in each core plate disappears more promptly than in the solid core. Moreover, since the two core holders at the opposite ends of the core are formed of the non-magnetic material, magnetic fields are not readily generated between the core and magnetically soft components around the core during operation of the solenoid actuator, which contributes to reduction of energy loss. Thus, the core of the invention makes it possible to ensure high energy efficiency of the solenoid actuator. Further, the plurality of core plates are only required to be simply stacked in the predetermined direction and fixed in a state sandwiched between the two core holders by the fixing means to form the laminated stack. This makes it possible to make the construction of the core simpler than that of the conventional laminated core, which contributes to reduction of manufacturing costs.
Preferably, the two core holders have end faces with which the armature attracted by the plurality of core plates is brought into abutment during the operation of the solenoid actuator, and wherein the end faces of the two core holders are positioned such that the end faces of the two core holders are flush with armature-side end faces of the laminated stack of the plurality of core plates, or closer to the armature than the armature-side end faces of the laminated stack are.
According to this preferred embodiment, during the operation of the solenoid actuator, the armature attracted by the plurality of core plates is brought into abutment with the plurality of core plates and the two core holders at the same time, or into abutment with the two core holders alone without being brought into contact with the plurality of core plates. Therefore, part or most of the impact caused by the abutment of the armature on the core can be received by the core holders. Particularly when the armature is brought into abutment with the two core holders alone without being brought into contact with the plurality of core plates, most of the impact can be received by the core holders. This makes it possible to prevent breakage of core plates even when they are thin, thereby enhancing the durability of the core plates.
The above and other objects, features, and advantages of the invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings.